Overcharge Bugged?

Hi just got the game a few days ago and loving it! Definitely has the potential to be a really good game.

Can you please explain how the overcharge card works? Currently, I'm in a game and have 3 momentum out of 6 left in my turn. I'm assuming overcharge should allow me to play it and, regain all my momentum back to (6-2)=4?

However, it won't allow me to play the card and indicates there are no viable targets.